The invention relates to a method for the removal of oxygen from water, especially from reservoir drinking water, and for preservation purposes. It is generally known that oxygen dissolved in water corrodes steel. It is therefore necessary to protect containers, pipes, steam boilers, heat exchangers, and other parts from corrosion by adding a reducing agent and to maintain the corrosion protection at low temperatures during cut-off periods or when first put into operation. This applies to closed apparatus systems as well. The invention is especially suitable for use in low temperature zones and includes the removal of oxygen from gases containing oxygen.
Various methods are used for the removal of oxygen dissolved in water.
Sulfites are, for example, used as reducing agents. They have the disadvantage that they are oxidixzed into sulfates, which results in an undesired concentration of salt. Additionally, corrosive gases, such as sulfur dioxide, may develop at higher temperatures. For this reason, hydrazine has been used as a reducing agent for a long time, being converted into innocuous nitrogen by oxygen. It is disavantageous, however, that a satisfactory reduction occurs only at higher temperatures. This disadvantage has been eliminated by using activators, which are generally added to the aqueous, approximately 10-25%, hydrazine solution. Quinonoid compounds, aromatic diamines, aminophenols, sulfonic acids and heterocyclic compounds are especially noted (DE-PS 1 521 749, DE-PS 2 601 466, DE-PS 2 115 463). These activators are disadvantageous in that they have to be used in relatively high concentrations of approximately 0.1 to 0.3 volume weight percent and higher, in relation to the aqueous hydrazine solution, resulting in high expenses. Additionally disadvantageous is that organic compounds can diffuse into the vapor phase, causing complications when using vapor as processing vapor. A further disadvantage is that a narrow pH-range of 10.0 to 10.4 has to be maintained to assure high reaction velocity. Setting of the pH-value has to be ascertained by continuously adding alkali. Many of the suggested activators are too expensive for practical use.
It has further been suggested to use manganese, copper, cobalt or vanadium compounds (U.S. Pat. Nos. 4,022,711, 4,079,018, 3,764,548). These, however, have the disadvantage of low activity or can cause undesired corrosion themselves. Furthermore, they cause the hydrazine to decompose during storage. Even if one eliminates these disadvantages by adding complex compounds of these metals with organic ligands as complex constitutents by using, for example, cobalt maleic acid hydrazide (DE-PS 2,232,548) or cobalt (II)-complexes with 3,4-diaminotoluene, 1-amino-2-napthol-4-sulfonic acid, or pyrocatechin (DE-PS 2,639,955), there will still be the need for relatively high concentrations at high pH-values. Thus, the problem with organic components cannot be solved in this fashion.
Organic activators exhibit the additional serious disadvantage of having their effectiveness reduced in conjunction with the time involved during removal of the oxygen. Attempts have already been made at using inorganic activators by adding small amounts of iodine or bromine, or the salts of the acids of these elements, to the hydrazine solution (DE-PS 1 186 305). It is disadvantageous in that the water, the oxygen content of which is to be eliminated, has to be filtered through an active coal filter following mixing with active hydrazine in order to assure a satisfactory oxygen reduction, requiring additional expenditures. The low reaction velocity of hydrazine, activated by iodine or bromine, with oxygen dissolved in water, is an additional disadvantage.
It is an object of the invention to remove oxygen dissolved in water by using hydrazine as a reducing agent, as well as using activators which eliminate the necessity of using organic compounds as activators, the invention requiring very low activator amounts, having a broad pH-range, allowing the removal of oxygen at high reaction velocity without diminishing oxygen removal over time, allowing processing at low as well as at high temperatures, and eliminating the need to treat the aqueous phase with active coal.
It is the object of the invention to develop a suitable activator using hydrazine as a reducing agent for the removal of oxygen dissolved in water, with the activator containing no organic components, being effective in small quantities, assuring a high reaction velocity at low temperatures with a broad pH-range, and with the hydrazine not decomposing during storage and maintaining its effectiveness during the removal of oxygen with advancing time.